In the related art, image forming apparatuses, such as copying machines and printers, includes a sheet feeding apparatus that feeds out a sheet toward an image forming unit. Such a sheet feeding apparatus includes a liftable intermediate plate, and a feeding roller, and is adapted to lift the intermediate plate by the rotation of the feeding roller to press a sheet on the intermediate plate against the feeding roller, and feed out the sheet as the feeding roller rotates in this state.
Here, as a configuration for lifting the intermediate plate by the rotation of the feeding roller in this way, for example, there are those adapted to fix a cam to a rotating shaft of the feeding roller and to bring this cam into pressure contact with a pressure-contact portion provided at the intermediate plate biased by a spring (refer to Japanese Patent Application Laid-Open No. H3-102019 and Japanese Patent Application Laid-Open No. H10-153247). If a feeding operation starts, the intermediate plate is lifted by the rotation of the cam while opening the spring pressure of a spring that biases the intermediate plate, and a sheet on the intermediate plate is the pressed against the feeding roller.
Incidentally, in such a sheet feeding apparatus of the related art, the ascending speed when the intermediate plate ascends by the rotation of the cam is determined depending on the force of the spring that biases the intermediate plate and the outer peripheral shape (profile) of the cam. Additionally, the ascending speed of the intermediate plate, in other words, the speed at which the top sheet of the stacked sheets abuts against the feeding roller varies depending on the stack amount of the sheets on the intermediate plate, and the speed in a case where the stack amount is small increases more than the speed in a case where the stack amount is large. In a case where the speed at which the top sheet abuts against the feeding roller in this way has increased, an abutment sound (collision sound) is generated when the sheet abuts against the feeding roller.
Here, in order to reduce this abutment sound (collision sound), the rotating speed of the cam, in other words, the rotating speed of the feeding roller may be made slow to make the ascending speed of the intermediate plate slow. In addition, in a case where the rotating speed of the feeding roller is made slow, there is a concern that an image cannot be suitably formed on a sheet. After this, however, if the rotating speed of the feeding roller is increased to the printing speed (process speed) of the image forming apparatus, an image can be suitably formed on a sheet.
However, in order to allow such speed control, it is necessary to drive the feeding roller by a dedicated driving source. However, generally, a driving source often serves also as other driving sources of an image forming system and a conveyance system. In this case, the feeding roller cannot be rotated only at a constant speed. For this reason, only the rotating speed of the feeding roller cannot be made slow, and if the printing speed increases, the rotating speed of the feeding roller increases and the ascending speed of the intermediate plate also increases correspondingly.
That is, in the sheet feeding apparatus of the related art, the driving source of the feeding roller serves as other driving sources. Thus, it is not possible to arbitrarily change the rotating speed of the rotating shaft to abate the abutment sound. For this reason, although the elevating speed of the intermediate plate depends on the profile of the cam, there is a limit of sufficiently securing the reduction region of the ascending speed of the intermediate plate only by the outer peripheral shape of the cam.
Thus, the invention has been made in view of these circumstances, and an object thereof is to provide a sheet feeding apparatus and an image forming apparatus that can reduce the collision sound when a sheet abuts against a feeding roller and suitably form an image on the sheet.